Dungeons and Dragons is a very niche game. Only a select group of people would even be willing to try it, and only a few of that group would be willing to invest in the long haul. The problem with that is that it's a great game that I would argue everybody could enjoy, provided they have the right group of people to play with.
The biggest problem is that it's nigh impossible to find the group that has the proper synergy. I've played Dungeons and Dragons intermittently over several years at this point, but I haven't really played in a campaign that lasted longer than a few months. I play with the same group of friends, sure, but for whatever reason we always stop after (on average) about eight sessions. (This still translates to probably about thirty two hours of total play time, but for a long term game this is nothing.)
D&D is difficult. It's a very complex game that requires at least a dungeon master that has an in depth knowledge of how the structure of the system mechanics works. But with the proper devices, a world can be created. It is the dungeon master's job to create the world in which the game is being played, but it is the job of everybody else at the table to jump in and help everybody else in, too.
Dungeons and Dragons is at its best when everybody is playing their role. It is the most fun when the people at that table stop becoming the players, and become the characters. It's fun when I, a deceptive, evil Drow, blatantly lie to my brother sitting next to me, in character, about something that is occurring in the game. In real life of course, we know what is truly happening, but my brother's character may or may not know that I am lying to him, and this discrepancy can create some hilarious stories and memories later on. It adds to the immersion, and is the main reason I find D&D fun.
For example, today my character disguised himself as a guard, and was found out practically immediately by one of the party members. Later on, he told the rest of the party about how I was effectively lying to them, but, since my character was unaware of this, he kept on with the charade, disguising himself later in the day and feeding them more misinformation. My character is deceptive and manipulative, trying to get as much out of every situation as possible. But as irony goes, he was the one that was deceived. This made every aspect of my in character would-be deception hilarious, and that is the core reason why Dungeons and Dragons is amazing.
Long term, this game attaches you to these characters. Matt Mercer and a bunch of other famous voice actors stream a campaign of their own, and they've been doing it for a few years now. Since they have grown so attuned to these pretend characters, you can see that in a way, they really are those characters. In a few parts of the show, where a character looks like they are about to die, you can really see how it affects everybody at that table.
Imagine the moment where your favorite character in any show died. Remember that moment where you felt the most anguish you have ever felt for that fictional character. Now imagine that having been your character, or your best friend's character. Your party of adventurers has grown attached to that one person, and losing them would not only affect the characters, but naturally it would affect everybody at that table. Of course, people can rejoin the campaign as a new character so they don't get left out on the gaming sessions, but it won't be the same.
More than any game, expansion, or any other past time, I want a group of friends with which I can achieve that sort of emotional connection with. But it's not easy to find.